Calibration is the typical way to ensure the position accuracy between the industrial robot and its tool or between the industrial robot and its work object in the industrial robot cell. In particular, the tool and the work object may be defined with inaccurate kinematical data. So that, a good calibration makes it possible to align the off-line program with the on-line, and it can also recover the cell once the relative position between robot and the tool or the work object gets changed.
Currently, manual cell calibration by the field engineer is relatively time-consuming and inaccurate. For high accuracy demanded applications, it can easily take days' effort for a cell commissioning or recovery on customer site.
U.S. Pat. No. 7,684,898 describes a method for calibration of a working point (TCP) for tools on industrial robots with a calibration device includes the use of at least two light barriers with an azimuth angle greater than zero at an angle to each other and intersecting at an intersection point. The method includes fixing set TCP positional coordinates for a set working point for the tool, relative to a tool reference point and a TCP coordinate system relative to the working point, moving the tool to the set working point with relation to the TCP coordinate system through the light barriers, such that the tool tip interrupts the light barriers, recording actual TCP positional coordinates determining the difference between the set TCP positional coordinates for the interruption of the light barriers for a set working point and the corresponding recorded actual TCP positional coordinates for the actual working point, calculating the actual working point from the set working point for the number of levels of light barriers from the differences and the known position and azimuth angles (a) of the light barriers. This calibration method requires the knowledge of the position and azimuth angles of the light barriers, however this method requires a pre-defined tool data and can only work with one posture without covering post inaccuracy introduced by the manipulator.